Animals eat one another without qualm; civilized men consume one another by due process of law.

—Will and Ariel Durant, The Lessons of History, 1968

A nation's sinew begins to tear. Triumph in one group is met with fear and bewilderment in another. Old prejudices are reanimated; new ones are invented. The masses succumb to irrational forces, prodded to frenzy by politicians and the media. The nation is poised to devour itself.

The controversial election of Donald Trump as the forty-fifth US president polarized the United States more than any other time in its contemporary history. To those watching, it seemed remarkable, and yet the partisan division was a familiar enough scenario, even in the “United” States. The 1960s saw police and the right wing clash violently with the leftist counterculture and with the civil rights and anti–Vietnam War movements. In the 1950s, McCarthyism drove the nation into repression, fearmongering, and political paranoia. Panic over Communism destroyed countless Americans’ careers, or saw them wrongly imprisoned for treason. A century before, the American Civil War drenched the nation's soil with the blood of over 600,000 people, greatly as a result of disagreement over slavery; even in the twenty-first century, bloody clashes between the Left and Right have erupted over the place of Confederate monuments in America. All of these schisms have been grounded in partisan psychology. Such Left-Right divisions are old, seen all over the world, and, in some form or another, certain to continue.

But why are these periods of conflict so common across nations and history? To truly understand the turmoils of today we must look somewhere most of us are unaccustomed to looking—our primordial past. Our current political struggles are ancient, rooted in a time before we even had nations, and indeed before we were fully human. What I will show you in this book is that the difficulties we face forming cohesive societies in the modern era reflect psychological adaptations with a simple, ancient purpose—keeping our ancestors alive in savagely dangerous environments. All too often these adaptations are at odds with the environments in which we currently live. This mismatch between the ancient and the modern is at the core of what divides us along political lines. While we will excavate far below the landscapes of our political parties in search of answers, political partisanship will remain a key framework because when nations turn against themselves, a reliable fracture opens between the political Left and Right.

To begin to understand this fracture, let's turn to an unlikely source for psychological insight: media pundits. American political commentator and talk show host Chris Matthews once described Republicans as the “Daddy Party” and Democrats as the “Mommy Party.” Writes Matthews,

Republicans protect us with strong national defense; Democrats nourish us with Social Security and Medicare. Republicans worry about our business affairs; Democrats look after our health, nutrition and welfare. Republicans control the White House; Democrats provide a warm, caring presence on Capitol Hill…it's the traditional American family. “Daddy” locks the door at night and brings home the bacon. “Mommy” worries when the kids are sick and makes sure each one gets treated fairly. This partition of authority and duty may seem an anachronism from the Leave It to Beaver era, but it's an apt model for today's political household.1

Similarly, in a play on John Gray's best seller on the differences between men and women, Men Are from Mars, Women Are from Venus, the meme Republicans Are from Mars, Democrats Are from Venus has recently echoed across the popular press.2 Hardline conservative commentator Ann Coulter even boasted on Fox news, “I am more of a man than any liberal.”³ As it happens, these observations are far more empirically accurate than we might have imagined.

Naturally not all men are conservatives, and not all women are liberal. In fact, research suggests a link between partisanship and gendered psychology.⁴ The term gender often describes masculine or feminine traits that may be expressed independent of sex and very often honed in their expression by culture. But even though gender can exist independently of biological sex, as we will learn throughout this book it is not independent of biology. Neither is politics.

To help us safely foray into this treacherous crossroads of gender, sex, and politics (as we move forward, religion will also cross this path), let us proceed with the understanding that in the grand scheme of human psychology, men and women, and liberals and conservatives, exhibit far more similarities than differences across innumerable psychological indices—daddies also worry when the children are sick, and mommies too bring home the bacon. Nevertheless, we venture into the slivers of difference, for those slim terrains abound with explanatory information about our evolved political psychology. The old adage that one should never discuss sex, politics, or religion in polite company would suggest that hazarding there could be fraught. Given the outlandishly controversial status of evolution, in America anyway, this topic may have a similar impact. But even a casual read of the history of political division reveals that the consequences of not understanding are far worse than the discomfort of knowing.

This book is about how Stone Age mating gave rise to our political orientations. More specifically, it is about how evolution programmed our minds with mating strategies to help us reproduce amid a fierce field of competition, how men and women employ different strategies to achieve reproductive fitness (i.e., representation in the gene pool), and how political partisanship arises from these sex-based approaches to perpetuating our genes. More precisely, I explain how all the hallmarks of political conservatism—its tribalistic flavor (us versus them), its emphasis on female sexual control, and its hawkish and territorial nature—are rooted in male mate competition, the ageless biological struggle for reproductive dominance. Far exceeding the scope of any government sex scandal, male competition for women turns out to be the core driving force behind contentious political issues as wide-ranging as affirmative action, social welfare, gender equality, contraception, abortion, taxes, criminal law, and foreign policy. Even the winner-take-all mentality of conservative economic policy is based on male competition for mates.

War, by necessity, is a critical focus of this book because it is rooted in team-based male-mate competition, and because our evolutionary forensics finds its crimson fingerprints all over our gendered political orientations. The risk of being annihilated by the outside tribe—and the potential gains of taking over the rival tribe's territory, resources, and women—forged the coalitionary psychology of men. Here I will show you how the militaristic logic embedded in that psychology maps squarely onto all the hallmark values of political conservatism. It is from the context of violent male mate competition, and its most heightened expression, war, that we are able to most fully understand the masculine tenor of conservative political psychology, along with the set of complex emotional responses that are roused in the conservative clash with the Left.

What I also reveal is that the roots of liberalism, too, are far older than we imagined, having arisen from the timeless effort to rein in dominant males and to prevent them from monopolizing resources and impinging on the evolutionary fitness of those with less power. More fundamentally, liberalism is based on the prodigious human task of rearing offspring, a critical survival enterprise championed by women, and provisioned by the “Mommy” parties of the world. We will review, among many other evolutionary dynamics, striking evidence suggesting that male competition has impelled some women to adopt conservative ideals as a means of competing with other females, making alliances with dominant men, and producing sons who are themselves strong male competitors.

And so the political insights offered by the commentators quoted above begin to acquire novel explanatory power when seen through the lens of evolutionary psychology, a field that rests on the understanding that we humans have spent 99 percent of our history in small bands of hunter-gatherers, living in environments very different from those in which we currently reside. Survival in those environments was harsh, with perpetual threats from predators, starvation, disease, and violence from outside tribes. These are the environments in which our political predispositions evolved. And because our current circumstances comprise only a blink of an eye in our evolutionary history, we retain psychological adaptations for that ancestral world. What this ultimately means is that the dark-suited men who represent us in government wield the power to steer the global economy, shift the parameters of human liberty, or unleash the devastating machinery of war, and they do so using Stone Age brains. This basic fact of human psychology is equally true for the women increasingly moving into positions of political power, and for the masses of people who elect our leaders.

But critically, having a Stone Age brain in the modern era poses certain challenges. Even though the risk of being massacred by neighboring tribes has drastically diminished since our perilous days as hunter-gatherers, our minds remain calibrated for ancestral environments that roiled with intertribal bloodshed. And as we grow into a vast, interconnected community of nations, bound by a global economy, our capacity to rain destruction on our neighbors grows commensurately. And so today we maneuver our way through precarious foreign and domestic policy arenas under the influence of these ancient and often volatile calibrations. But through evolutionary science we have an opportunity to better understand the primal workings of our evolved minds and to better transcend our most destructive political urges.

THE EVOLUTIONARY MODEL: WHY, HOW, AND CAVEATS

Disentangling the ravel of human politics may seem a daunting task. Today the political machine spans a vast, interconnected community of hundreds of nations around the globe, controlling billions of individual human beings. Adding vertiginous complexity to an unfathomable scope, politics are conducted with a stunning degree of bureaucratic intricacy, veined with deception, confounded by continuously shifting alliances, obscured by the conflicting commentary of partisan analysts, and steered by behind-the-scenes maneuvering of wealthy political stakeholders. This political machine is a colossal, dimensioned, dynamic web of human interaction that is often difficult to comprehend.

But evolutionary science is in the business of distilling complex processes down to their most basic elements. It does so by illuminating the ultimate reasons for everything that we love, abhor, think, and do, including the political policies we support, whether we are liberal or conservative, or whether we are inspired or repelled by the words of a president.

Understanding evolutionary science, though, requires an unflinching gaze in the mirror. Often revelations we find in evolutionary approaches can be surprising and, for some, a bit unnerving. There are those who worry that in accepting our evolutionary psychology we somehow concede freedom to our genes. However, there are endless examples of how we are able to reject the hand that nature dealt us. Eyeglasses, automobiles, computers, vaccines all reflect our ability to transcend our genetic limitations—here in vision, speed, endurance, mental computation, and resistance to disease—and the list goes on and on, from the simplest household items to entire fields such as medicine. And certainly, without an understanding of our evolved psychological impulses, we are more, not less, likely to enact them without consideration.

Using evolutionary psychology to understand human behavior can also require navigating tricky cognitive and emotional terrain, in particular avoiding common logical fallacies. One common pitfall is known as the moralistic fallacy, which occurs when we assume that undesirable qualities of nature simply cannot be true. Linguist and cognitive scientist Steven Pinker offers an illustrative description of how this fallacy emerges:

The moralistic fallacy is that what is good is found in nature. It lies behind the bad science in nature-documentary voiceovers: lions are mercy-killers of the weak and sick, mice feel no pain when cats eat them, dung beetles recycle dung to benefit the ecosystem and so on. It also lies behind the romantic belief that humans cannot harbor desires to kill, rape, lie, or steal because that would be too depressing or reactionary.5

Political liberals may be more likely to commit the moralistic fallacy, which may sound like the following: gender equality is desirable—therefore any psychological differences observed between men and women must be a priori false; war is morally wrong—therefore we cannot have instincts for it. This fallacy is partly what makes conservatives dismiss liberals as ignorant or naïve about the way the world really is.

But the inverse of the moralistic fallacy, the naturalistic fallacy, assumes that what is natural must be moral or desired, and it is equally to be avoided. Writes Pinker,

The naturalistic fallacy is the idea that what is found in nature is good. It was the basis for social Darwinism, the belief that helping the poor and sick would get in the way of evolution, which depends on the survival of the fittest. Today, biologists denounce the naturalistic fallacy because they want to describe the natural world honestly, without people deriving morals about how we ought to behave (as in: If birds and beasts engage in adultery, infanticide, cannibalism, it must be OK).⁶

As you may have guessed, political conservatives are more likely to commit this kind of fallacy. Examples may sound something like the following: men are naturally physically stronger than women, therefore women should be subordinate to men; warfare is instinctive, therefore it is acceptable. This fallacy is partly what makes liberals see conservatives as coldhearted and cynical. There are evolutionary reasons for adopting one or the other of these fallacies, as I will later explain. But for the time being, the goal is to avoid either of them.

The other challenge is in seeing psychological impulses that are usually hidden from conscious awareness—for example, becoming aware of the powerful drive to reproduce our genes, which we normally take for granted as simply the desire for a sexy partner, or love for our children. Eminent evolutionary psychologists Leda Cosmides and John Tooby refer to this phenomenon as instinct blindness.7 We are often blind to our evolved predispositions, which are so ancient that they work seamlessly in the background while directly affecting our foreground behaviors and ideologies. The evolved reasons for our political behavior can be counted among those difficult-to-see processes. We can observe examples of political instinct blindness in media interviews where voters holding fervent party, leadership, or policy stances are stutteringly unable to articulate reasons for their strongly held positions when queried. This reflects more than just deficits in political literacy; it also reflects politics’ deep channels into primitive emotion centers of the brain that operate below the level of conscious awareness.

In order to overcome instinct blindness, American psychologist William James suggested in 1890 that we must make “the natural seem strange.”⁸ In other words, we must strive to achieve reflexive distance from processes so natural that they're usually taken for granted. Others have suggested we take the perspective of an imagined Martian anthropologist studying humankind, with no preconceived notions of how human beings should think or act. These are great suggestions. Empirical research is another means to overcome instinct blindness because it can isolate in the psychology lab what may be difficult to see in the flow of everyday living. Because political views are so prone to bias, with political bias often being a form of instinct blindness, using the objective lens of science to understand our political selves is even more crucial. In examining the evolutionary psychology of human politics, we will therefore draw heavily on scientific research and also examine parallels between political behaviors among humans and other species, which can help to illuminate evolutionary processes that are difficult to see in ourselves.

But don't our politics simply reflect the values we're taught as children or the political ideas we were exposed to? Aren't they a matter of where we grew up or where we live? Most people tend to think of their political views as carefully considered choices they have made—perhaps reflecting the influence of particular experiences or people in their lives. There is no question that parents serve as important filters of information to their children and that they impart (or try to) their moral, religious, or political perspectives. Equally, there's no question that our cultural surroundings profoundly influence how we think, what we teach our children, and how we publicly express our political views.

Yet the picture is not as simple as we once thought. An increasingly large body of research is finding a genetic component to our political natures. Twin studies are one such branch of study. Identical twins, who share nearly 100 percent of their genes, show high concordance in their political orientations and more concordance than nonidentical twins, who share only half their genes.9 Even more revealing, however, are studies of twins reared apart. Research has found that monozygotic (identical) twins reared apart have virtually the same likelihood of sharing a political orientation as those reared together.¹⁰ In other words, the influence of upbringing doesn't seem to matter among identical twins—genetically similar individuals hold remarkably similar political views despite having grown up in different households and despite not being influenced by one another growing up. When political orientations of nonidentical twins reared apart are examined, concordance drops off dramatically.¹¹ Overall, meta-analytic research suggests that 30–60 percent of the variance in our political preference is due to genetic factors.¹²

This in no way means that we are genetically programmed political automatons. Simply put, our ability to adapt to environmental circumstances would seem to underlie at least 40 percent of the variance in how we normally behave politically. This adaptability is what makes human political psychology so complex; it's also what allows the possibility of modifying our political stances when they no longer serve us.

Moreover, political parties themselves can and do shift over time. For example, before the 1980s, the Democratic and Republican parties in the United States were less ideologically polarized than they are today, which means that not only did the parties share certain characteristics but also that there was greater within-party variation—i.e., a wider liberal-conservative spectrum within both parties. Several historical factors have been identified that have been pulling the parties apart, for example, the rise of ideologically driven media interests (like Fox News) and conservative talk radio networks in the 1980s and 1990s, and the rise of coalitions between economic conservatives and religious fundamentalists in the 1970s.13 Also influential was the civil rights movement of the 1960s and 1970s, which spurred mass defection of white Southern Democrats to the Republican Party.

And so in our efforts to understand the psychology of political orientation, we should not place excessive weight on party affiliation—political parties are subject to shifting and realignment. However, parties fall along a Left-Right continuum that is itself exceptionally stable; the ability to identify oneself on the Left-Right dimension has been reliably demonstrated across nearly every human society. As one example, the World Values Survey Association (WVSA), which is run by an international team of scientists and scholars, collects a mammoth amount of survey data on values and beliefs across the globe. Between 1981 and 2008 the WVSA asked over 250,000 people from ninety-seven countries to identify themselves along the Left-Right political spectrum with a question: “In political matters, people talk of the ‘left’ and the ‘right.’ How would you place your views on this [ten-point] scale, generally speaking?”¹⁴ Across this ethnically, geographically, religious, technologically, and politically diverse sample, nearly 80 percent were able to place themselves along this dimension. When graphed, the results of this enormous survey show that endorsement of Left-Right political orientation forms a natural curve.

Like other variables of the natural world, the universality of the Left-Right dimension and the fact that orientation falls along a natural curve suggest that survival adaptations are at the core of our political leanings. If we look for these adaptations, as we will throughout this book, we discover the bones of our ancestors undergirding the modern body politic. In order to understand these adaptations, a deep dive into the biology of being liberal or conservative is in order.